Dogs in Diapers for Incontinence
Riggs did very well even though his kidneys were failing, but near the end, it came down to a few more weeks with diapers or tolerate pee from one end of the house to the other. He no longer had control and would pee and walk trying to get outside. It wasn't his fault - he tried, but the control just wasn't there. If he thought about peeing, he just did it. 
To solve this problem we needed an inexpensive solution as purchased "doggy diapers" were much too expensive for a dog his size (120 lbs.). We also needed something that could contain a LOT of urine. What we came up with were human Depends type diaper pants, with an overnight maxi pad tucked into the front. It worked quite well. We changed it about 2-4 times a day.
We joked about the ruffles on a manly dog...but the elastic was helpful in keeping them in place. The only modification needed was a large tail hole that went below the anus (in case he pooped, we'd rather clean it off the floor than fur) and an elastic band (shown below) with tabs on each end to keep the diaper up. These I purchased at the dollar store and they were meant to keep the corners of the bedsheet on the mattress but worked great for securing the diaper.
The other alteration I did to the diaper was because Riggs was male. This probably wouldn't be as necessary for a female. Since the majority of urine went "forward" I added a high-absorbency maxi pad just in front of the diaper's absorbent layer. Most pads have a sticky tab and that hold it in place. With males there is also the option of a 'belly band' specifically for male dogs.
Hence, relatively cheap, disposable diapers for a BIG dog. This could be modified for use on a smaller dog...just get children's pull-up diaper pants. Once the pee would get heavy, the diaper would tend to sag and eventually fall off - but the extra elastic strap would keep it in place until we could change it and also allowed him to be more mobile - getting up, sitting, lying without the diaper falling off.
A few excellent tips I discovered helped dogs with diapers and keeping your house smelling good:
1. Buy a black light. Urine lights up when you point a black light at it, getting an inexpensive black light wand is a great investment so that you know where to clean.
2. Stock up on enzymatic cleaners - I like Nature's Miracle or Four Paws, but there are many brands to choose from. Enzyme cleaners break down the proteins in urine and stool, which removes the smell - which is more effective than just deodorizing.
3. Have a mop handy (or whatever you use for accidents)...because they will happen. The sooner you can clean them up, the less damage they'll do.
4. Buy some elastic straps (like those used for keeping sheets on the bed) for giving extra support in holding up a heavy diaper.
For dogs that are less mobile, you might be able to use pee pads. A dog that can hold it long enough to get outside but has mobility issues too is a good candidate for a wheelchair or sling.
